Vehicle brake



Apri129, 1941.- H, HUNT 2,239,916

VEHICLE BRAKE Filed June 26. 1959 3 Sheets-Sheet 1 650,965 h. HUN 7' l ATTORNEY.

April 29, 1941. Q H HUNT 2,239,916

l VEHICLE BnAKE V Filed June 26, 1939 3 Shets-Sheet 2 .656. 64 7/A '504 5 e 55 @567707275 )T K t; Iii. j y INVENTOR 550,965 H HUA/7` I 55 BY v Y 0J w76 9 y y @Wa/1y@ ATTORNEY.

pril 29,1941. Q H HUNT f 42,239,916

VEHICLE BRAKE u y Filed June 2e, 19:59 v :Smets-sheet 3 650665 H. HUA/7 y ATTORNEY.

Pu'atented Apr. 29, 1941V 'George H. Hunt, Lansing,

Corporation, corporation of Michigan Motor Wheel Mich., assignor to Lansing, Mich., a

application June 2s, 1939, serial No. 2s1,i11v

(El. 18S-78) Y g consists of a novel brake shoe servo control de- 7 Claims.

'I'his invention relates to brakes for vehicle wheels, and particularly to brakes of the type in which one shoe exerts a servo action on the other shoe.

Vehicle brakes of the type defined above usually comprise a pair of semi-cylindrical brake shoes which are-arranged to iloat slightly in al circumferential direction relative to the backing plate,v

and have their ends opposite the operating mechanism connected together in such a manner that a part of the force exerted by the rotating brake drum is picked up by one (primary) shoe and applied through the aforesaid connection to the other (secondary) shoe. 'Ihis eiect is commonly called a servo action. Thetotal braking elect of the ltwo shoes is thus increased manytimes over what it would be it there were no such servo action.

The advantage, that is, the increased braking effect of the ordinary brake of this type is to a large extent offset by several disadvantages. These disadvantages are the greater wear on the secondary shoe than on the primary shoe; the

' necessity for' providing different kinds of linings on the two shoes; and the unequal distortion olf the drum when the brakes are applied.

The rst of -these disadvantages, that is, the .increased wear on the secondary shoe, is due to the fact that the pressure on the secondary shoe is several times greater than thatof the primary shoe, and as a result,` the increased friction between the secondary shoe and the drum causes f the lining of the secondary shoe to Wear out prematurely.

Another disadvantage inherent in the ordinary servo brake is that if the linings of the two Eshoes have the same coefficient of friction, and this is of normal value, then the brake tends to become erratic and'diiilcult to control on account o1' the high ratio of servo effect relative to pedal` pressure.' To avoid thisand give satisfactory effectiveness and control it has been necessary to use a lining on the secondary shoe which has a much lower coellicient of `friction than that of the primary shoe.

i The third disadvantage listed above is that of distortion of the drum when the brake shoes are actuated.A 'I'his is due to the fact that the pressure on the secondary shoe being greater than thaton the primary shoe, there Ais a tendency to .force the drum-to one side of its normal center and cause it to become Voval or eccentric.-

The present invention has foiits primary objects the overcoming of theaforementioned disadvantages. In its broadest aspects the invention vice which is interposed between the ends of the brake shoes opposite the brake actuating mechanism and so constructed that only a denite portion of the effort of the primary brake shoe is transmitted to the secondary shoe. of the effort is applied to the brake backing plate and has no effect oncthe brake shoes or brake drum.- The advantages of this structure lie in the equalization of the wear of thebrake shoes; the substantial elimination of unequal drum distortion; the possibility of using brake linings on both shoes khaving the same coeilicient of friction; and

V the decrease. oi'movement of the brake operating pedal required to take up the slack in;l the system. Other objects`v of the invention will become apparent in the following specification when read in connection with the accompanying drawings,

in whichg Figure ly is a cross-sectional view of acomplete4 brake assembly taken on substantially the line I-I ofFigure 2; i a

Figure 2 is a cross-sectional view taken on substantially the line 2`2 of Figure 1;

Figure `3 is a cross-sectional view of the servo control device shown in Figure 1, but on a larger scale and shown in braking position;

Figure 4 is an end elevational view of the control device shown in Figure 3; l

Figure 5 is a cross-sectional view oi a modifiedform of the invention taken on substantiallyv the line 5 5 of Figure 6;

Figure 6 is a cross-sectional view of the brake shown in Figure 5 taken on substantially the line 6.-6 of Figure 5; i

Figure '1 is an enlarged cross-sectional view of the servo control shown in Figure 5, but on an enlarged scale; I l

Figure 8 is an enlarged end elevation of the control shown in Figure 7;

Figure 9` is a cross-sectional view of the brake adjusting mechanism taken on substantially the line 9-9 of Figure 5; yFigure 10 is a sectional view of a still further modined form of the invention taken on sub# stantially the line Ill-I0 oi' Figure 11;

Figure 1-1 is across-sectional view taken on substantially the line II-il of Figure l0;

Figure 12 is a cross-sectional view of the servo control device shown in Figures 10 and l1 taken on substantially the line iZ-Il ofFigure 10;

Figure 13 is a cross-sectional view of the control taken on substantially the line I3,`|3 of Figure 12; and

Figure 14 is a fragmentary sectional View of The rest the structure shown in Figure 13 with the flange ll9a omitted. y

Referring more specifically to the drawings, andparticularly to Figures 1 to 4, there is shown a complete wheel brake mechanism which com 4prises a conventional brake drum I0 having a backing plate Il. Adjacent the periphery of the backingplate is an anchor pin i2 which is secured thereto by'means of a nut I3. A pair of semi-cylindrical shoes I4 and Ilia, which are provided with any suitable brake lining It, are mounted `on the backing plate li within the brake drum lll. The upper adjacent ends of thek brake'y shoes are recessed to receive and bear against the opposite sides of the `anchor pin i2.

Normally the adjacent ends of the brake shoes It Vand maare held against the anchor pin by i means of a pair of coiled springs i8 and' tft. These springs it and it are secured at their adjacent ends to the anchor `pin` and at their remote ends to the respective jbrake shoes.

secured to the backing plate is the brake operating mechanism. This mechanism is al conventional hydraulic device comprising a wheel'cyl-vv `indexl 2i secured to the backing plate il by any suitable means. Slidable within the cylinder 2l is a pair of opposed pistons 22. The latter are held in spaced relation by a coiled spring 2?. The remote en ds or the pistons receive a pair of lstruts 23a, the remote ends of which are bifurcated to receive the radial flanges of the shoes I4 and Ha in a manner well known in the art.

The wheel cylinder 2i has an inlet at one side thereof which is connected by a suitable conduit to a master cylinder, not shown, of the brake system, in order that hydraulic nuid may be forced into the wheel cylinder temperate the br.

Secured to the backing plate it by bolts 2da.

'at a. point directly opposite the anchor pin and operating mechanism is a brake servo control, which constitutes the heart. of this invention. It includes a housing 2d having two axially Valigned cylinders 2t and 2t therein of did'erent diameters. The cross-sectional raree. oi the larger cylinder 25 is approximately .2% times that of the smaller cylinder t; although the cio and has rigidly secured to it a' spring 36 which engages any one of the notches 32 in the periphery of the nanged head 3l. Y

A dust Acover 35-is iitted over the end of the housing, and is frictionally held thereon by means of a tight fitting peripheral ilange 36. A pluralityof integral tongues 31 are struck from the main body of the cover and are received in complementary recesses 38 in the plunger 2l. The interlocking connection between the tongues 3i and recesses 38 prevents relative rotation' of the plunger 21 and housing 2t, and the cover itself excludes dirt and moisture from the interior of the housing.' The brake shoe it, may be adjustedto compensate ior wear of the lining it by turning the screwg. The'sprlng ad yields to allow such rotation but prevents accidental turning of the screw.

' Wlthin the cylinder 25 is a plunger 3s having a radial ange di at its outer end which overlles abuts the adjacent end of .the

arid normally housing 26. The ilange M allows the plunger 39 to move `axially to the right, as viewed in` Figure 3, but preventsmovement to the left from its normal position. The plunger 39 has a rubber cup washer $0 to prevent leakage of iiuid. The flange 4i is notched at t2 to receive tongues 43 which are struck from an annular ring t frictlonally engaging the housing. The

ring ed prevents rotation of the plunger B9.

.An adjusting screw B5 having aanged head igis threaded into a, recess in the plunger 39 and receives a biiurcated strut 4t which is adapted to be connected to the flange of the brake shoe ita. A spring 41 is attached to the strut 48 and engages notches E9 in thel flanged head 'of the adjusting screw. This adjusting the same as the adjusting' mechanism previously described in connection with the plunger 27.

, The portion of the housing 24 between the two plungers 2l and 89 is filled with brake operating fluid. However, there is -noconnection between the housing 2d and the brake applying system or any of the wheel cylinders. Fluid need he added only to replenish that which may be losti through accidental leakage.

The lower ends of the brake shoes it and ita are biased toward each other at all times by a coiled spring @da which is secured at its remote ends `by ,the respective shoes. Due to the iact relative diameters oi the .two cylinders may be varied within reasonable limits. The housing 2d has an opening in one side by which it may he filled with brake uid. This opening is ordi@ narily closed by a screw plug den.

Within the cylinder 2d is a plunger 2l which ts snugly yet slidably therein. The inner end that the plungers 2t and te are of diierent diameters, the spring normally holds the ge di of the plunger t@ against the adjacent end of the housing, andl thus in the position shown in Figure i.

The operation of the structure described is as follows:

when the trakteren een rotating in the direction shown by the arrow in Figure l, and it of the plunger 2 is provided with a cup washer 2B of rubber or other material to prevent leakage past the plunger. An adjusting screw 2t having a stem 29a threaded'into the recess Sii (in the plungerrf1 and 'aiiianged head ti, is provided -to compensate for bralreshce wear. The hanged is desired to stop the rotation ci the same. the foot pedal ci the brake system' is depressed in the usual manner and iiuid. is forced from the master cylinder into the wheel cylinder 2 i, thereby tending to `force the pistons 2t apart. Bes

l cause the spring it? is weaker than the spring it,

shoe it `(which is the primary shes when the b drum is rotating in the direction er the arrow) head 3i is notched about its periphery'as lat 32 for a purpose which will appear presently.

A strut 33, bifurcated at its outer end, is seated within recess in thehraire adiusting screw will be pressed into contact with the brake d. and there wili be a tendency icr the snm td te move inthe' same direction es the dnn, 'or f counter-clockwise as viewed in Figure i. mere is also a tendency tor shoe it to roch the tert about its ecnnettcn with the etwa mechanism vis identical with and its operation is what is usually spoken of as a Iself-energizing drum and wm exert Ma cannot exert servo action It. There will I3 oi the servo control. Thus, the brake shoe tends to dig into the brake drum I0, producing wrapping or action. Thus, a greater force plunger 21 than would be produced from the action of the operator on the master cylinder alone. This pressure is then transmittedy by the iiuid in the servo control housing tothe smaller plunger 39, andthenee to the secondary shoe Ila Due to the fact that is exerted on the the plunger 39 is smallerthan the plunger 21,v

only a portion 'of the force applied by the shoe I4 is transmitted to the shoe Ma. I'he rest of this force is transmitted to shoulder 26a of the housing 2t. As indicated above, the ratio of the force exerted by the shoe I4 to that applied to the sh As soon as the shoe Ma is-pressed into engagement with the drum Ill, it will tend to rotate counter-clockwise', but this rotation is prevented by th'e of the shoe lla with the-anchor pin i2. Therefore, the shoe I4 energizing" action the same as shoe il, but there ism no servo action from shoe Ha to shoe iti.

When the brakes are released the springs is, i9 and 69a return tion shown inV Figure When the vehicle is reversing, or in other words, when the drum iii is rotating in a clockwise direction, as viewed in Figure i., brake shoe Ha will be pressed into engagement with the y a self-energizing action the same as the shoe i tated in the other direction. However, the-shoe on shoe it because the iiange 4i of the plunger 39 is in engagement with the adjacent end of the housing 2li.' Therefore, all the pressure on the shoe it is received fromV the actuating mechanism 2u, and there is no self-energizing or servo action on the shoe and a pair of brake shoes i and 52 having conventional linings 53 and 5t. These shoes are bth T-shaped in cross-section for the reception of an anchor pin cella is approximateengagement of the uppery end a has. a wrapping or self-` When the drum is ro` The latter is Vsecured to a brake backing r and absorbed by the the parts to the initial posi- K plate 51 by means of the anchor pin 59 which is inserted in stud 59 is offset anchor pin 55 in order 'I'he other end of the anchor pin 56 is slotted at oi' a nut 58. The inner end 56 is reduced to form a stud the opening 55. This slightly from the axis of thel to form an eccentric.

60 to receive a screw driver or similar tool for turning the pin', whereby of the brake shoe plate 51 by means of an to adjust the upper end initially. The other shoe 52 is secured in a similar manner to anchor pin 6i identical to the pin 56 butlocated diametrically opposite the pin 56, and received/in an opening Gia in the flange 52a.

Intermediate the upper ends of the brake shoes is the brake operating mechanism. -Itconsists backing plate 5'! wheel cylinder is suitable conduit,

der of the brake system.

Within the Wheel posed plungers 63 and t apart by means of a ts is recessed at 58 to adjacent end oi the has a peripheral iian normally abuts the to prevent movement of active position 'toward th der, es viewed in Figure 5.,

.recess which is threaded bralre adjusting' screw 'iii li has a notched peripheral end whereby the adjacent end of the pensate for lining wear.

has a recess to receive a cylinder 52 isa pair of opt provided with i'ubher Bti, respectively. and 'biased coiled spring ai. Piunger receive a tongue 5s on the brake shoe di. plunger 2 at its outer end which end of the wheel cylinder the plunger from its e left or into the eylinu 'The piiinger has 'a the reception oai' the The adjusting screw -fiange iii at its outer be turned 'to brake shoe 52 .te solli-a The adjusting screw it tongue U. on the adia-e for cent end of .the braire'shoe Acoiied ends to the brake shoes draws [the adj each other. end tov theV brake shoe 52 the backing plate 5i. This acent ends of the brakes A coiled spring spring iti is'. connected at its remote respective anges 55a and 52a of the toward a is secured one d at its other end te spring .tends to hold the brake 52 in its inoperative position even after the outward movement o commenced.

` The Servo controi is located between opposite 'the wheel f the brake shoe mechanism in this structure the ends of .the .brake shoes cylinder 6E. It comprises a housing is having two axially aligned cylinders it and lo oiA diierent diam tached to the .backing plate 5i?. cross-sectional areas oi .the cyli is approximately 2% described modification Slida-ble within the eters and is rigidly The ratio of .the

nders T anni 1, as in the previously f this invention.

cylinder il is a plunger 'it which carries a cup washer '19a of rubber or siniilar material ito prevent l plunger. The plunger l eakage of iiuid past .the 9 is alsofpr'ovided with a threaded recess 8i for the reception of a threaded adjusting screw 82. The a; peripheral iiange 83 n cessed at 84 to receive a' cent end of the brake shoefl. ,i 18 by means of a screw Secured to the housing adjusting screw 82 has otched at 83a, and is rey `85 on the adja- 'tongue ual rotation thereof. S

4pletely through the side crew 8.5 extendsk comwallpf the housing it the backing and into ,a longitudinally extending g-roove 88 in the plunger 'i9 whereby to prevent rotation of the latter yet lallow axial movement thereof.

The cylinder` 'I8 slidably receives a plunger 89 having a cupnwasher 89a thereon. The plunger t9 is recessed at 9| to receive a -tongue 92 on the adjacent end of the brake shoe 52. A thin metal dust cover 99 is secured to the plunger 89 to exclude dirt and moisture from the housing.

Both brake shoes 5I and 52 are held in properly `spaced,relationship to the 1backing plate 51 yby a pair of guide pins 94 whichI are secured to the backing plate. A pair of pins 95 and coiled spring et hold the brake shoes against the guide pins 94.

The operation of thisl modification is as follows:

When uid is forced into the wheel cylinder 62 is' transmitted to the brake shoes fby means of a pair of truts |06, similar to struts 23a, previ ously described. 'Ihe brake shoes are normally -held against the anchor pin ||J3 by means o coiled springs |01 and |08.

The servo control mechanism isshown best in Figures 12 and 13.v It consists of a housing |09,

having a generally cylindrical bore extending longitudinally therethrough. ends of the housing 09 is a pair of recesses |||I and Pivoted in these recesses on pivot pins j l I2 and H3, respectively, is a pair of short levers from lthe master cylinder, the plunger 63 is. pushed y to the left as viewed in Figure 5 and acts on the tongue 69. As the oval opening in the ange 5ta of the shoe 5| is considerably larger .than the'y anchor pin 56, the brake shoe may move into contact with the rotating brake drum, and as soon as it touchesthe brake druml l there will .be a self-energizing action, the same as that in the primary shoe of the 4previously described device.

Shoe V5| will then rotate counter-clockwise, exerting a force on the plunger i9 which force is in part transmitted to the plunger 89 and to the adjacent end of .the brake shoe 52.

` The oval opening in the web 52a of the brake shoe 52 allows the latter to move slightly in a i and ||5. These levers are of the cross-sectional shape shown bestlin Figure 12, and in their normal position the free ends ||6 and lll touch the body portions of the complementary lever.

Slidable within the bore of the housing l|09 is a pair of plungers l I8 and H9. Theseplungers are of generally cylindrical cross-section, but are provided along one side of each with a groove which is keyed to the interior of the housing |99 'to` prevent yrotation thereof while allowing the plungers to slide axially of the housing. Norxnally, the adjacent ends of the plungers H8 and H9 contact the remote' surfaces of the levers iid and ||5 respectively.

counter-clockwise direction and exert a :torcev with self-energizing effect on the brake drum 5t. The upper end of the shoe 52 is held'against movement by the flange 72 of the plungerl. it will thus 'be apparent that basically the operation of this brake is identical with thatprevously described. In other words, when the drum i@ operates counter-clockwise, brakeshoe 5| is? selfenergized and' exerts a servo action on brake shoe 52 and brake shoe 52 is then seli-energid" butdoes not exert any servo action on braise shoe 5i.

When the drum rotates clockwise, brake shoe 52 is self-energized, but because-.oi its contact with the anchor pin 6l, no force is transmitted to .the shoe 5|. Neither is there lany self-energizing action of the shoe 5|.

The shoes are initially'adjusted by loosening the nuts 58 and turning the anchor pins 5e and 6| to position the shoes in the drum. The posiv tioning is done by eccentric 59 on pin 5t and a corresponding eccentric on pinA El. Clearance between the lining and the drum and adjustment for lining wear is obtained by rotating the adjusting screws fl! and 82 in the desired Adirec-l tion.' v l In Fi es 10 to 14 is shown a still di'eren't' yembodiment ofthe invention; The basic diner-'- ence between the construction shown in Figures 10 to 14 and that shown in Figures 1 to 4 lies in the fact that the servo controldevice is mechant; cal rather than hydraulic.

The general arrangement of the'v brake and 'its operating mechanism is identical with that Threaded into arecess in the outer end of theplunger M8 is a brake adjusting screw |20, the outer end o which ls hanged radially at |2|. This ange 62| is provided with a. plurality ofperipheral notches.l lzla, asshown best in Figure ll. The brakeadjusting screw is provided lwith an axially extending recess in which a strut |22 is received. This strut is bifurcated at |23 to receive the adjacent endof the'flange oi theA brake shoe tdi. Non-rotatably attached to the strut '|22 is a resilient spring. |24 which yieldably bears against the outer periphery ofthe flange 29 zand seats in any one of the various notches y |2|a about the circumference thereof.

The plunger lthas a ange lita at its cute-r end which abuts the adjacent endv of housing it@ except when thelplunger il@ has moved to the right. frire plunger are is provided 'with e brake adjusting screw |25 having a anged head |26 similar to the ange |36 of the other adiust=' ing screw. The adjusting screw |25 is recessed to receive a strut |21 wi'rlch 'receives the adjacent end of the brake shoe |02, and this strut |21 has associated with it a resilient spring |28.y

The housing m9 has a support extending lat,-

Aerally from one side thereof lin the form of a plurality o! brackets |29 which are bolted to the f backing plate by means of bolts |313.

In a-general way the operation of the modiiication shown in Figures 10 to 14 is identical to that shown in' Figures l todi except that, as above pointed out,` the eiort received from the primary brake shoe |0| is transmitted by lthe'l mechanical linkage above described to the secondarybrake shoe |92. In other Words.. when liquid is introduced under pressure into the wheel cylinder IM, the shoe i9| is forced into contact shown in Figures 1 to 4. The brake construction comprises generally a brake drum |90; a pair of semi-cylindrical brake shoes |0l/ and |02, Van

anchor pin m, and a nyarauncbrake wheel cylinder .IBL Within the cylinder is a pair or pistons Ill (only oneof which is shown) which are yforced apart by fluid introduced into "the wheel cylinderyfrorn the master cylinder, .not

shown. '.The torce exerted on the pistons |85 75.

with the amm. and men tends to' rotate counterclockwise. The blower' end ofthe brake shoellll.

then 4pushes the strut |22, itsassoclated screwl I29,'a.nd plunger H8 against the lever' H4, tending .torrotate the latter-counter-clockwise about its pivot |l'2.V It will benoted that as soonesthere has been any rotation oi' the lever IH, the

end||1 ofthev lever lllbreaks awaykfrom the lever H4, and all the force iromtlever lil is applied to .lever ||5r through the free' end ils ot the lever IM. Lever lli' is then rotated clock,

Intermediate the the torce applied to the plunger lis'is consider' ably less than that applied` to the plunger H0 by the brake pedal |0|. By suitably proportiom.` ing the links IM and H5, any desired ratio of forces can be obtained. 'I'he preferred ratio oi forges is approximately 2% to 1. That is, lfor each 2% pounds of-force exerted on plunger ill but one pound is transmitted to the brake shoe The modication just described is so, designed that when the br .drum rotates clockwise, or in other'words. when the vehicle on which it is used is reversing, the shoe |02 cannot exert a servo action on shoe |0|. Flange ||9a on the plunger Il! prevents that eiIect. It will beevident, however, that the flange il 9a may be elimihated, as shown in Figure 14, allowing shoe |02 to act as a servo shoe if desired, for in. this embodiment of. the invention `vthe fonce which would be derived by shoe |0| from shoe`-|ii2--when the drum rotates clockwise would be the same as thatobtained by shoe |02 from shoe |0| when the drum rotates counter-clockwise. In that respect the device shown in Figures to 13 would operate differently than the two previously described structures if not prevented from doing so by :dange ||9a.

From the foregoing it will be seen that the above described invention makes it possible to exactly equalize the pressures exerted on both brake shoes and yet allow the brake shoes to be so arranged that they are self-energizing when v the brake drums are rotated in a forward direction. As a result, the brake lining oiboth shoes can be the same, .and it is unnecessary to experieilort applied to one of said plungers by its associated brake shoe is transmitted to the other plunger.

2. A unitary brake shoe servo control comprising a tubular housing, a; pair of plungers within said housing, one of said plungers being siidable axially of said housing in either direction, and the other plunger being siidable in one direction only from its normal position, said plungers being adapted to be connected at their remote ends to the respective adjacent ends of a pair of brake shoes, and means intermediate the adjacent ends I of the plungers for transmitting a predetermined portion of the eiort applied to one of said plungers by its associated brake shoe to the-other plunger.

3. A unitary vbrake shoe servo control adapted to be secured to the backing plate of a brake assembly between the adjacent ends of a pair of brake shoes, said control comprising a tubular housing. and me'cnism within said housing adapted lto be connected to the adjacent ends of the brake shoes for transmitting a part of the ment with diiferent kinds of brake linings in order to ofl'set the excess pressure on the secondary shoe in conventional brakel constructions.

' Also, the force exerted on the brake drum by the shoes is applied in such a way that thereis no appreciable eccentricity ot the drum.

The various modincations disclosed in this application are shown by way of illustration only. It will be evident, however, that various other changes may be made in the structure by those skilled in the art. and accordingly, the scope or the invention is'to be limited only by the apalms- Pendedl ate the adjacent ends oi' sai plungers. each of said levers engaging the adjacent end oi the complementary plunger intermediate the ends oi' the lever. the free end of one of said levers engaging the other lever at a point intermediate'its pivot and its point oi contact with its' associated plunger whereby a predetermined portion of the nected to the backing plate. y

5. A brake assembly comprising a backing plate, primary and secondary brake shoes, brake applying means acting on the brake shoes at one 6. A brake assembly comprising a backing plate, primary and secondary brake shoes, brake applying means acting on the brake shoes at one the brake shoes and engaging the remote sides of the levers at points intermediate their ends.

7. A unitary brake shoe servo control comprising a tubular housing.- a pair oi' piungers within v'Gr.oaoiiz H. HUNT. 

